Comparative genomic analysis provides insights into the genetic diversity and pathogenicity of the genus .

Some spp. are important pathogens. According to the latest prokaryotic taxonomy, the genus consists of facultative intracellular parasitic species and extracellular opportunistic or environmental species. Intracellular species include classical and nonclassical types, with different species generally exhibiting host preferences. Some classical intracellular species can cause zoonotic brucellosis, including , , , and . Extracellular species comprise opportunistic or environmental species which belonged formerly to the genus and thus nowadays renamed as for example or , which are the most frequent opportunistic human pathogens within the recently expanded genus . The cause of the diverse phenotypic characteristics of different species is still unclear. To further investigate the genetic evolutionary characteristics of the genus and elucidate the relationship between its genomic composition and prediction of phenotypic traits, we collected the genomic data of from the NCBI Genome database and conducted a comparative genomics study. We found that classical and nonclassical intracellular species and extracellular species exhibited differences in phylogenetic relationships, horizontal gene transfer and distribution patterns of mobile genetic elements, virulence factor genes, and antibiotic resistance genes, showing the close relationship between the genetic variations and prediction of phenotypic traits of different species. Furthermore, we found significant differences in horizontal gene transfer and the distribution patterns of mobile genetic elements, virulence factor genes, and antibiotic resistance genes between the two chromosomes of , indicating that the two chromosomes had distinct dynamics and plasticity and played different roles in the survival and evolution of . These findings provide new directions for exploring the genetic evolutionary characteristics of the genus and could offer new clues to elucidate the factors influencing the phenotypic diversity of the genus.